In an electric circuit of a motor vehicle including a battery that is charged by an alternator driven by the vehicle engine, when heavy current loads are applied while the engine is idling or going slowly, the mechanical load which is then suddenly applied to the engine by the alternator runs the risk of disturbing rotation of said engine, and may even cause it to stall.
This problem is becoming more severe as present day motor vehicles are being fitted with more and more electrical accessories (electrically-driven controls and servo-controls, heating, air conditioning, etc. ...) that draw large amounts of current.
A known solution to this problem, that occurs readily to the person skilled in the art, consists in immediately increasing the idling speed of the engine as soon as heavy current demand is observed, with this being done by suitably controlling the carburetor or the injection system to enable the engine to cope with the sudden increase in mechanical load applied to it by the alternator.
Unfortunately, that solution is quite undesirable since it makes designing control of the engine admission system much more complicated; in addition, it requires a functional link between two portions of the vehicle, namely engine admission and the alternator/battery circuit, which may have design origins that are completely different. The design process is thus made less flexible.